An electromagnetic filter is an apparatus for removing magnetic particles suspended in feed water by magnetic attraction to the magnetic material filling the internal space of a filtering column and is used in such applications as the removal of magnetic particles, for example, of iron oxide contained in the condensate from a power station. The electromagnetic filter further includes an electromagnetic coil disposed around the filtering column filled with the magnetic material, and a rectifier for supplying a direct current to the electromagnetic coil. For the purpose of removing magnetic particles suspended in feed water, the rectifier is used to convert an alternating current into a direct current, which is supplied to the electromagnetic coil. The magnetic flux so produced serves to magnetize the magnetic material within the filtering column. Then, feed water is passed through the filtering column, so that magnetic particles suspended therein are entrapped by magnetic attraction to the magnetic material. After the amount of magnetic particles entrapped in the magnetic material has reached an appreciable level, the passage of water is discontinued and the supply of a direct current to the electromagnetic coil is shut off to demagnetize the magnetic material. Subsequently, the magnetic material is cleaned with water or air so that the magnetic particles entrapped in the magnetic material may be expelled from the filtering column. In this manner, the passage of water and the cleaning operation are performed alternately.
The magnetic materials suitable for use in electromagnetic filters include ball-shaped magnetic materials, spiral magnetic materials, woolly magnetic materials, and the like. However, these magnetic materials have their own merits and demerits. Thus, it is most preferable to use spiral and woolly magnetic materials arranged in a large number of alternating layers.
However, if the filtering column is simply filled with a large number of alternating layers of spiral and woolly magnetic materials, lower layers of woolly magnetic material undergoes compressive deformation under the weights of the overlying spiral magnetic materials and, hence, the porosity thereof is reduced to interfere with the entrapment of magnetic particles. Moreover, this arrangement has the disadvantage that troublesome operations are required for placing the magnetic materials in the filtering column and/or removing them from the filtering column.